A great thing to do, especially if you are short on time, is to take the hop on/hop off bus tour of Barcelona.

The bus runs on three routes and all intersect at one point or another. There is the blue route which stops at places like: Teleferic de MontjuÔc, World Trade Centre, Museu d'Historia Catalunya, Parc de la Ciutadella - Zoo and Barri Gotic. The red route stops at: Passeig de Gracia - La Pedrera, Sagrada Familia, Park GŁell and Futbul Club Barcelona (Camp Nou). The green route is the shortest and goes to: Platja del Bogatell - Cementiri del Poblenou and Forum.

If you only have time to go along one of the routes, I would suggest the red route. And especially recommend hopping off and having a look at Park GŁell and the Sagrada Familia.

It's better value for money to get a pass for two days, and you can hop on and off all of these routes as much as you like in that period (You can also book via the website and it is a few euro cheaper).

Adult:1 day: 20 Euro.2 consecutive days: 26 Euro.

Child:1 day: 12 Euro2 consecutive days: 16 Euro

You can buy tickets on the bus, or at the tourist stand on Las Ramblas. You also get a little guide book with a short paragraph about the stops, and a book of discounts for activities in Barcelona. While on the bus you also get headphones and there is a running commentary available in 6 languages.